26 Jun BCHM 100 Assignment 4 In class we have discussed how enzyme
Question
BCHM 100 Assignment 4
In class we have discussed how enzyme assays can be used to determine the enzyme kinetic
constants Vmax and Km but in this assignment you will do the reverse. You will use known
Vmax and Km values to calculate expected rates for a pair of enzyme catalyzed reactions.
Suppose that you are provided data about phenylalanine hydroxylase and phenylalanine
aminotransferase (the enzyme that converts phenylalanine to phenylpyruvate in patients with
PKU). You are told that the Vmax and Km values for phenylalanine hydroxylase in a standard
enzyme assay are 100 µmol min-1 and 10 µM respectively, and those for phenylalanine
aminotransferase are 10 µmol min-1 and 1000 µM respectively.
Prepare a table that reports expected values of enzyme velocity (v) at the following substrate
concentrations ([s]): 1, 2, 6, 10, 20, 40, 60, 100, 500, 1000, 2400, 5000 (all values are in µM).
Prepare Michaelis Menten plots that illustrate these kinetic data. Dont forget to carefully label
the axes.
Now consider this pseudo-clinical case of two patients with PKU. Assume that the production of
phenylpyruvate by phenylalanine aminotransferase at a rate of less than 1 µmol min-1 as
measured by this assay can be handled by the body (the phenylpyruvate is converted to
something non-toxic or is excreted) and does NOT cause PKU.
A patient with mild PKU comes to the clinic with a blood phenylalanine concentration of
500 µM. When his phenylalanine hydroxylase is assayed as described above, Vmax and
Km values are found to be 100 µmol min-1 and 5000 µM respectively. Prepare a
Michaelis Menten plot for his enzyme as described above using the same substrate
concentration range. To what extent has the change in Km affected his enzymes ability
to convert phenylalanine to tyrosine, assuming that the substrate concentration it sees
is the same as the patients blood phenylalanine concentration? At this blood
concentration of phenylalanine, at what rate is his phenylalanine aminotransferase
producing phenylpyruvate? Is this rate consistent with a diagnosis of PKU (that is, is it
above 1 µmol min-1)?
A patient with strong PKU comes to the clinic with a blood phenylalanine concentration
of 2400 µM. When her phenylalanine hydroxylase is assayed as described above, Vmax
and Km values are found to be 2 µmol min-1 and 10 µM respectively. Prepare a Michaelis
Menten plot for her enzyme as described above using the same substrate concentration
range. To what extent has the change in Vmax affected her enzymes ability to convert
phenylalanine to tyrosine, assuming that the substrate concentration it sees is the
same as the patients blood phenylalanine concentration? At this blood concentration of
phenylalanine, at what rate is her phenylalanine aminotransferase producing
phenylpyruvate? Is this rate consistent with a diagnosis of PKU that is more severe than
the first patient?
Complete the assignment and submit it to Michael Melesse ([email protected].edu). This
homework assignment is due by 11:59 p.m. Monday November 24, 2014. Late submissions will
be penalized at a rate of 5 points per day.
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